1. Field of the Invention
The present invention relates to an addition-curable type fluorosilicone gel composition which has excellent solvent resistance and thixotropy and which, upon curing, gives a gel-like cured product.
2. Description of the Prior Art
Silicone gels are excellent in such properties as electrical insulation properties, stability of electrical properties, flexibility and so forth, and are in use for potting or encapsulation of electrical and electronic parts, for example, as a material for coating control circuit elements such as power transistors, ICs, capacitors, etc. to protect the elements from thermal and mechanical troubles.
With the advent of semiconductor-type pressure sensors utilizing the piezoresistance effect of a silicon chip, in recent years, application of electronics to sensor technology has been investigated and practiced more and more in a variety of industrial fields. For instance, the semiconductor-type pressure sensors mentioned are used as an air quantity sensor for fuel injection control in automobiles, a gasoline vapor pressure sensor in gasoline tanks, and as a water or gas pressure sensor in hot water supply systems. These pressure sensors, however, have the problem that the sensor characteristics would be changed if an electrode part is corroded by corrosive components in a measuring medium with which the sensor comes into contact or a contaminant deposits on the surface of a pressure-sensitive chip. Thus, there is a request for development of a protective material which can protect the sensor elements without adversely affecting the sensor characteristics. Such protective material is fundamentally desired to have high purity and to produce no adverse effects on sensor characteristics by, for example, surface hardness, shrinkage on cure, or swelling with solvent. As a material for meeting these requirements, silicone gels with excellent solvent resistance have come to draw attention.
Where a silicone gel is used as a protective material for a semiconductor-type pressure sensor, it is necessary, for example, to apply a gel-forming silicone composition (silicone gel composition) to the surface of the sensor by spot potting. Known silicone gel compositions, however, are high in fluidity, so that they are not suited for use in spot potting and cannot form an effective protective layer on the sensor. Thus, there is a demand for a silicone gel composition with low fluidity, for use as a protective material for the above,mentioned semiconductor-type pressure sensors.
Besides, where the fluidity of a silicone gel composition is lowered by simply increasing the viscosity thereof, the viscosity is lowered when the composition is heated for curing, so that it again is impossible to obtain an effective protective layer on a sensor of the above-mentioned type.